The present invention relates generally to apparatus for weighing a vehicle in motion, and more particularly to such apparatus employing fiber-optic sensors and switching mechanisms for determining the weight and other characteristics of the vehicle in motion including the number of axles, weight distribution on the axles, wheel base, axle width, number of tires on each axle, weight distribution on the tires of each axle, speed of the vehicle, and tire footprint.
At the present time the weighing of vehicles is primarily achieved by using static weighing systems utilizing hydraulic load cells and/or mechanical lever mechanisms. The use of such static weighing systems is fairly common at truck weighing stations and at mining and agricultural facilities. However, recent efforts have been made to provide vehicle weighing systems that are capable of accurately determining the weight of a vehicle while it is in motion since many benefits can be derived from such a capability. For example, in the transportation industry the use of weigh-in-motion systems on the various highways traveled by trucks and other heavy vehicles would be highly beneficial since such vehicles would no longer be required to stop at weighing stations using static weighing systems and thereby significantly reducing law enforcement costs associated with the installation, maintenance, and operation of such road side weighing stations. Further, the dangers associated with the roadside weighing stations as created by the truck traffic in the area of the weighing stations will be obviated. Also, airports for commercial and/or military air traffic would benefit from the use of a relatively low cost, weigh-in-motion system. For example, at a commercial or military air field a weigh-in-motion system placed on the taxiway could be used to weigh the aircraft prior to take-off so as to instantly provide the pilot and control tower personnel with information pertaining to the weight of the aircraft as well as the weight distribution on the individual axles and tires of the aircraft for promoting inflight safety and enhancing fuel efficiency. Additionally, the replacement of the static weighing systems usually employed at mines, agricultural, and landfill sites with weigh-in-motion systems would considerably expedite the weighing process and increase the operational efficiency of the facility.
There are several varieties of weigh-in-motion systems currently available which use various types of mechanisms for weighing the moving vehicle. The most common of these weighing systems rely on piezoelectric sensors, hydraulic load cells, bending plate strain gauges, linear variable differential transformers, and capacitive mats. Hydraulic load cells and bending plate strain gauges are considered to be the more accurate of these mechanisms while the systems using piezoelectric sensors and capacitive mats are considerably less expensive than the systems utilizing hydraulic load cells. However, the presently available systems using piezoelectric sensors and capacitive mats have not been found to be capable of providing the desired level of accuracy required for many weigh-in-motion applications.
Recent developments in weigh-in-motion systems utilize fiber-optic mechanisms in the system for determining the weight of the moving vehicle. For example, in U.S. Pat. No. 4,560,016, an optical-fiber grid embedded in a rubber pad is placed on the roadway in the path of the moving vehicle. When a vehicle passes over the pad, the dynamic weight of the vehicle is imposed on the pad and the optical-fiber grid contained therein to bend or pinch the fibers through an array of bending and/or pinching fixtures to attenuate the light passing through the optical fibers. By calculating the amount of light attenuation, the weight at each axle of the moving vehicle can be determined with the combined weight at the various axles being indicative of the total vehicle weight. This patent is incorporated herein by reference for its discussion of previously known weigh-in-motion systems and the teachings therein pertaining to fiber-optic technologies including the electronics for transforming the optical signals provided by the bending of the fibers into the calculated weight of the vehicle in motion.
While the aforementioned patented system represents a considerable departure from the mechanism usually used in weigh-in-motion systems, there are still several desirable goals to be achieved in order to assure accuracy of such systems for the weighing of vehicles in a wide range of vehicle weights. Also, it is desirable for such a system to have the capability of determining and/or identifying other physical parameters or characteristics of the vehicle being weighed, such as the vehicle speed, the number of axles, weight distribution, the number of tires on each axle, the weight distribution on the tires on each axle, fire footprint, and the wheel base of the vehicle.